Due to support requests recently, it has become obvious that Apple have mis-configured their mail servers, either intentionally or because they’re stupid (both are one and the same in this case, but I’m leaning towards the latter of course), so that they don’t play well with an anti-spam technology that NinerNet and millions around the world use called greylisting. (If you want to more thoroughly understand greylisting, we recommend you read the page at that link.)
It seems that some (many?) users of Apple-administered mail servers on domains like mac.com, me.com, icloud.com (maybe even apple.com itself) and possibly other domains that we’re not aware of receive bounce messages for email messages they send to NinerNet-hosted domains that contain this text:
<email-address@ninernet-hosted-domain.com>: host mx.niner.net[178.62.195.26] said:
451 4.7.1 <*****@*****************>: Recipient address rejected:
Intentional policy rejection, please try again later (in reply to RCPT TO command)
At this time we don’t know if this also applies to domains running on any of the servers that use an Apple operating system, but we haven’t seen evidence of this because even those servers generally run applications (e.g., Postfix [which we use], Qmail, etc.) that are not Apple products and comply with email standards. We also don’t know the frequency with which email sent to NinerNet-hosted domains fail.
Here’s the explanation we have sent to recent clients:
The four (hundred) codes (451 and 4.7.1) tell the sending server that the error is temporary, and that the sending server should (as it also says in plain English), “try again later”. A four-hundred error code is not a permanent error; those are five-hundred codes. Email messages should not be bounced by four-hundred error codes, so this is why the sending (Apple) server is behaving incorrectly according to email standards. Email doesn’t work if organisations (i.e., Apple) ignore standards.
Greylisting isn’t something we invented while I was bored last weekend; it’s an extremely widely used and also extremely successful anti-spam technique that we have been using for about as long as NinerNet has been in business, which is thirty years.
So the sender needs to bring this to the attention of the support department at Apple. NinerNet is not the cause of this problem.
As we’ve also explained, “standards” are not vague suggestions; they’re the “laws” on which servers and clients agree to operate so that they can work together.
In order to compensate for the stupidity of the brain trust at Apple we have whitelisted the following domains server-wide, so that greylisting is not applied to email from these domains:
- apple.com
- icloud.com
- me.com
- mac.com
This, of course, means that spam from these domains will more likely reach our clients, and for this we humbly apologise. We hope that Apple are doing a better job of keeping spammers off of their systems than they are at actually running the mail servers themselves.
If your correspondents on other Apple-hosted domains report similar problems sending email to you, please let us know and we’ll add those domains too to our mail servers’ whitelists.
If you have any questions about this, please feel free to contact NinerNet support. Thanks for your attention.
